The present invention relates to a pump apparatus for pumping melt metal from a furnace to a place where it is to be used, said pump apparatus comprising a pump of gas-plunger type having a container holding a chamber with an inlet for drawing molten metal from the furnace to the chamber via a suction pipe immersed in the furnace melt, and with an outlet for forcing molten metal out of the chamber to the place of use; a gas-operated suction and pressure system comprising a suction source with a vacuum pump, a pressure source with a compressor and a conduit provided with valve means for alternately connecting and disconnecting the suction and pressure sources, the gas pressure of the latter acting directly on the melt in the chamber inside the container; and a control system for controlling the pump apparatus, said container being vertically aligned and arranged immediately above and in line with the furnace, said outlet being arranged at the bottom of the container.
It is known through patent specifications EP-190 680, U.S. Pat. No. 4,010,876, DE-1 197 591, GB-1 596 826, U.S. Pat. No. 4,708,191, FR-2 061 708, DE-3 923 079 and JP-1 095 856, for instance, to keep components that are in contact with the melt heated, to protect the melt with an inert gas, to measure the level of the melt inductively or capacitively, and to use graphite of ceramic material for certain components that are in contact with the melt.
Each of the known pump apparatus is limited to its own specific casting process and, if they are of the pressure-increasing type the mechanical designs are so complex that they reduce operating reliability and service life.
The object of the present invention is to achieve an improved pump apparatus that is relatively simple in design, reliable in operation, pressure-increasing, has long service life and can be used for all usual casting methods and metals.
The pump apparatus proposed according to the invention is substantially characterized in that the inlet of the container is arranged at the bottom thereof; that valve means are arranged inside the container to alternately open and close said inlet and outlet; that the suction and pressure system comprises a closed circuit containing a vacuum tank, a pressure tank, a vacuum pump/compressor unit connected therebetween, and said valve means, and is connected to the chamber in the container via said conduit; and that said control system is arranged to alternately connect and disconnect the vacuum tank and pressure tank and to synchronously or substantially synchronously therewith alternately open and close said inlet and outlet.
The pump apparatus according to the invention offers several valuable advantages over conventional pump apparatus:
The entire pump is located above the melt. Only parts of the suction pipe and filter are located in the melt. PA1 The pump is pressure-increasing up to substantially the pressure provided by the vacuum pump/compressor unit. This improves the quality of the castings and increases productivity. Conventional systems for low-pressure casting produce approximately 1 bar. PA1 Thanks to a specific level-measuring system the level of the melt can be measured without any instrument coming into contact with the melt, and extremely accurate dosing is possible. PA1 A closed pipe system is used, thereby reducing oxidation of the molten metal. PA1 Simpler holding furnaces can be used. PA1 The working environment is improved since no open vessels containing melt need to be transported.
All parts of the pump apparatus according to the invention that come into contact with the melt are manufactured out of ceramic material, which is resistant to the melt (aluminium, for instance, is extremely aggressive to most materials) and withstands the temperature. All parts coming into contact with the melt are also surrounded by furnace modules and are thus heated. This prevents any "freezing" in pipes and pump. Like the factory furnaces, the pumps are heated during production stops and over weekends.
The pumping action is thus obtained by means of a gas-operated suction-pressure system. A vacuum pump/compressor unit is located between a vacuum tank and a pressure tank, this unit ensuring that the gas is evacuated in the vacuum tank and that a sufficiently high pressure prevails in the pressure tank. A valve effects the necessary switching between drawing up and forcing out the metal. Since the gas withdrawn from the pump is hot, it passes an accumulator where it emits energy. Similarly, the pressure-generating gas passes the accumulator and receives additional energy. This enables energy consumption to be as low as possible. The gas used is inert.
A system for lifting and possibly turning the pump valves is provided in order to regulate inflow and outflow of molten metal to the pump. Tests indicate that raising valves is to be preferred. The movement can of course be achieved using various types of drive sources.
The entire pump cycle is monitored by a control system, preferably a PLC. The advantage of the system is that flow and pressure are controlled throughout the cycle.
Thanks to the pump apparatus according to the invention being given the features described in claim 1 it can be used for all types of casting methods. It can therefore be connected to a place of use arranged, for instance, for casting melt in a mould, for dosing melt into a container in a die-casting machine, for dosing melt into a chill or sand form or for supplying melt through a die equipment of any desired profile.